The correct answer is A) pieces may fly off the chisel and injure your eyes. A chisel with a mushroom head should not be used because the deformed, mushroomed head can cause metal fragments to break off and potentially strike the user's eyes when the chisel is struck. The irregular shape of the mushroomed head makes it more likely for pieces to break off compared to a properly maintained chisel with a flat, square head. Using a chisel with a mushroom head poses a serious eye injury hazard, which is why it should not be used. The other answer choices are incorrect because: B) holding the chisel head is not the issue, C) the irregular shape can prevent square strikes, and D) the hammer head is not at risk of being chipped when using a mushroomed chisel.